PROJECT SUMMARY/ABSTRACT The identification of autoantigens in atherosclerotic plaques has prompted investigation of the antibody-mediated pathogenesis of atherosclerotic cardiovascular disease (ASCVD). One target of IgG antibody induction in ASCVD patients is apolipoprotein A-I (ApoA-I), the major protein of high density lipoprotein (HDL). Although anti- ApoA-I antibodies have been identified in mice and human subjects, their role has not been elucidated. Continued evaluation of the detailed antibody profile of ApoA-I will improve our understanding of the immune responses associated with ASCVD. The overall goal of this project is to elucidate the role of anti-ApoA-I antibodies and to characterize their molecular composition and functional impact in ASCVD. To achieve this goal, we will characterize the molecular components of the anti-ApoA-I antibody response in mice and patient serum samples and correlate these factors with cellular interactions, functional outcomes and atherosclerosis progression. The hypothesis is that anti-ApoA-I antibodies can exhibit a pro-inflammatory or anti-inflammatory effect, depending on the specific antibody characteristics (i.e., antigen engagement, subclass, epitope specificity, Fc receptor interaction), and these effects are exacerbated or suppressed in ASCVD patients. The rationale for this proposed research is that understanding one component of the humoral immune response associated with ASCVD will lead to a better understanding of the underlying mechanisms and improved patient outcomes. This hypothesis will be tested through two specific aims: 1) Elucidate the molecular components and functional implications of antibodies targeting ApoA-I in mouse models of atherosclerosis; and 2) Delineate the association between antibody profiles and ASCVD events in a large community-based prospective patient cohort. Aim 1 will employ novel immunomodulation strategies, developed in Dr. Venditto's laboratory, to achieve epitope-specific modulation of antibody responses to elucidate antibody/epitope function and role in atherosclerosis progression. In the second aim, sera from patients in the Multi-Ethnic Study of Atherosclerosis (MESA) will be evaluated for antibody profiles and correlated with patient outcomes. The approach is innovative due to the utilization of in vivo immunomodulation approaches that can alter the anti-ApoA-I IgG profiles, and our ability to achieve epitope- specific immune suppression in mice. The proposed research is significant as the outcomes of this research will improve our understanding of B cell-mediated immune responses to ApoA-I to elucidate the role of antibodies on ASCVD progression. Detailed characterizations of the antigen, epitope specificity, antibody subclass and receptor engagement will enhance understanding of ASCVD to guide therapeutic development and future efforts to improve risk stratification procedures in patients to decrease the burden of ASCVD in patients.